Candida albicans is a major pathogen in immunocompromised individuals, and disease often involves large numbers of organisms in the tissue. As a consequence, candidal antigen is known to escape into the circulation, and it is thought to modulate immune responses to Candida, and possibly to other agents. We have developed murine model in which circulating mannan (MAN) induces suppressor T (Ts) lymphocytes which suppress the development and expression of cellular immune (CMI) phenomena to candidal antigens. We have identified, by lymphoid transfers into immunized animals, Ts which are present in the spleens of naive animals 4 days following the i.v. administration of MAN (=4-day MAN Ts cell). The proposed research is designed to characterize this cell in more detail phenotypically and functionally, as well as to attempt to clone the cell. Phenotypic characterization of the uncloned cell will involve cell depletion studies, using various surface-specific antisera and complement, followed by attempts to transfer suppression to immunized animals with the depleted populations. Functional characterizations of the uncloned cell are designed to determine 1) its in vivo distribution in donor animals, 2) its specificity in vivo and in vitro CMI assays, 3) its potential to modulate CMI specific for the non-candidal antigens in transfer studies, and 4) its potential to modulate protective immunity when transferred to immunized animals. Phenotypic characterization of the cloned cell will involve labeling with fluorescein-labeled antibodies and fluorescence-activated cell sorting. Cloned cells will be examined functionally 1) in the transfer model, assessing MAN-specific and MAN-unrelated CMI, and 2) for potential cytotoxic activity against natural killer, allogeneic or mitogen- stimulated targets. Attempts will be made to determine if the cloned cells produce soluble suppressor factors and to characterize such factors with respect to ability to bind antigen and presence of Class II antigens. If cloning is unsuccessful, attempts will be made to dissect the suppressor cell cascade involved in MAN-induced suppression to search for afferent, transducer and efferent cells. Phenotypic and functional assays will be performed as described above, and attempts will be made to detect and characterize soluble suppressor factors. Underlying all of these studies is specific immunity to Candida, and since the nature of protective (acquired) immunity is poorly defined and controversial, we plan additional experiments in this area. Initially, attempts will be made to determine the role of L3T4+ cells in the development of protective immunity in vivo by treating animals with anti-L3T4 and determining their susceptibility. Attempts will made to expand, by mitogen stimulation, the pool of potentially protective lymphocytes, then use them to transfer protection. If transfer can be achieved with such cells, they would be phenotype.